1. Field of the Invention
The invention concerns devices for the summation or combination of N equiphase and equiamplitude microwave signals coming from N power amplifiers or channels. It also concerns these same devices wherein a microwave signal is distributed or divided identically on N channels or paths.
The last power stages of microwave transmitters, notably those used in radars, are increasingly being made by means of semiconductor devices. Since the power given by the semiconductors has not yet attained that of the tubes, there is provision for combining the output signals from several identical channels to obtain the required power by addition. This combination or summation can be achieved in different ways.
2. Description of the Prior Art
One of these ways consists in the use of a structure of the cascade-connected couplers type as shown in FIG. 1. This structure has, for example, a number k of series-mounted couplers/dividers Dk to Dl which divide the input power Pe in the ratios of 1/k and k/k+1 so as to divert a signal with a power of Pe/k+1 to an amplifier Ak with a gain G and a signal with a power of kPe/k+1 to the input of the next coupler.
The amplified signals are recombined by means of k couplers/combiners or adders, Cl to Ck, which have the same ratio, as defined above, for the couplers/dividers Dl to Dk, so as to add up the signals which are applied to their two inputs.
A structure of this type enables the use of the same semiconductor-based power amplifiers A0 to Ak, the output signals of which are combined in the couplers, Ck to Cl, so that the power Pe of the signal at the input of the structure is multiplied by a gain G.
This structure has the major drawback of having high insertion losses, so that its efficiency falls rapidly with the number of amplification channels used. Furthermore, it is necessary to obtain very precise coupling values, which are all the more precise as the number of channels is great.
Another structure which is used is that of the chandelier type, such as the one shown schematically in FIG. 2. This figure shows only the part corresponding to the combination or addition of the output signals of N=8 (N=2.sup.n) amplifiers A1 to AN, but it will be understood that the input signals of these amplifiers are obtained by a chandelier type divider system. The N output signals of the amplifiers A1 to AN are applied in twos to N/2=4 two-channel combiners, B1 to B4, which are known as "two-channel Wilkinson" type combiners. In turn, the N/2=4 signals resulting from the combination are applied to N/4=2 combiners, B5 and B6, and so on until there is only one output, that of the combiner B7 when N=8.
A structure of this type can be used to obtain efficient coupling among the different channels, but the insertion losses are proportionate to the number of series-connected elements.
A third structure used to make a combiner/divider is that of the radial type, implementing a so-called microstrip technology. As shown in FIG. 3, which gives a top view, it is formed by a circular substrate 1 made of a dielectric material which is metallized on the lower face. The upper face of the substrate 1 is divided into N=12 metallic sectors, each corresponding to a radial line, Sl to SN, which ends in a microstrip line Ll to LM, respectively connected to a terminal Dl to DN. The center of the radial sectors is coupled to a coaxial line (not shown). Resistors Rl to RN are connected among the different channels to absorb the difference in energies among the channels in the event of dissymmetry which might appear between the channels.
This structure has a high efficiency of about 95%, but it can be suitable only for relatively low power values of about 50 watts, in terms of mean value, and 1 to 2 kilowatts in terms of peak value at the center.
Finally, for greater peak power values, of the order of several kilowatts, a radial type of structure is used. However, this radial structure is one wherein the propagation of the waves takes place in a radial mode. As shown in FIGS. 4 and 5 which are, in the former case, a partially open top view and, in the latter case, a diametrical sectional view along the line V.V of FIG. 4, the structure has two parallel disks 10 and 11, which mutually define a circular space 12 that ends at the periphery of the disks by a wall 13. This wall 13 supports N =16 coaxial outputs 14, each connected to a coupler 15 placed on the internal periphery of the circular space 12. The top disk does not have any aperture, but the lower disk is open at its center to position a coupler 16, the central part 17 of which has a flared-out shape starting from a cylindrical bar 18, and a lateral part 19 of which has a cylindrical shape with a circular section, the rod/cylinder set forming a coaxial line.
In divider mode, the signals enter the center of the disk, and the flared part 17, called a "door knob", has the effect of gradually modifying the distribution of the electrical field so that it is propagated between the two disks 10 and 11. The density of the electrical field gets reduced with distance from the center, and the result thereof is a division by N when it is collected by N couplers 15.
Conversely, in combiner mode, wherein the signals are applied to the couplers 15, the electrical fields as well as the associated radial currents are increasingly intense towards the central part, and the result thereof is an addition of the signals applied, provided that these signals have the same phase and the same amplitude.
A device of this type is described, for example, in Bobby J. Sanders, "Radial Combiner runs Circles around Hybrids", Microwaves, Nov. 1980, pp. 55-58.
This type of structure is very efficient and enables the combination of many channels, N=110 in the above-mentioned article. It also enables peak power values of the order of several kilowatts to be obtained. However, the chief drawback is that the isolation between the channels is given by l0log 1/N, namely -13 db for N=20 so that, in combiner mode, the return wave received by a coupler 15, when several couplers are not powered, may be very high and may cause deterioration of the amplifiers in operation.
An aim of the present invention is to make a multichannel combiner/divider of the radial type, which has improved isolation so as to support an increased number of non-powered couplers, without any risk of deterioration in the amplifiers associated with the powered couplers.